This invention relates to the hydrolytic cleavage of O-sulfate esters of a group of antibiotics known as the thienamycins: ##STR2## both species I and II are antibiotics, wherein R is H or acetyl and M is H, an alkali or alkaline earth metal action or an organo cationic species such as pyridinium, and wherein the dotted line indicates saturated and unsaturated species. Starting materials I are known and available to the art. The final products are also known and available to the art. In addition to published references, starting materials I are disclosed and claimed in co-pending, commonly assigned U.S. Patent Applications Ser. Nos. 006,959 (filed 1-5-79) which is a continuation of Ser. No. 860,662 (filed 12-15-77) now abandoned; 860,665 (filed 12-15-77); 891,799 (filed 3-30-78) and 893,846 (filed 4-6-78); which are incorporated herein by reference.